Explosives are convenient sources of energy which can be suddenly released in order to perform work on various targets. Accordingly explosives have been applied for the breaking or cutting of solid materials, such as metal. This may serve purposes of demolition, separation of components of an integral structure or destruction of or damage to a target. In particular at sites which are difficult to access, or which are considered dangerous, the application of explosives may provide an outcome. Several methods of explosive cutting are known in the art.
A known method of explosive cutting is by means of shaped charges such as linear cutting charges. A linear cutting charge generally comprises a length of metal which is, e.g. substantially semi-circular of V-shaped in cross-section and an explosive which extends the length of the metal and which must be capable of sustaining detonation with a high velocity of propagation. The length of metal is arranged with its hollow side directed towards and spaced from the target metal to be cut, whilst the explosive extends centrally of and in contact with the opposite side of the length of metal. With a semicircular section length of metal the explosive, when detonated, acts on the length of metal to evert the length of metal and project a part of it as a high velocity metal jet at the target, the target thus being severed if the charge is sufficiently powerful. In the case of a V-section length of metal, the pressure exerted by the explosive, when detonated, serves to drive the two limbs of the V-section length of metal towards one another at high velocity so that they collide. As a result of the collision of the said two limbs a small part of each of the limbs is stripped off and is projected at the target as an extremely fast-moving blade-like jet which is capable of producing a very deep and narrow cut in a metal target for a given amount of explosive. Explosive cutting using shaped charges has disadvantages in that the application of a metal jet has low energy efficiency (a relatively high amount of explosive is required per cutting length), and that the jet may cause side damages if the jet shoots through the object to be cut after penetration.
A further known method of explosive cutting applies a shockwave refraction tape (SRT) in contact with the material to be cut [WO-A-86/07000]. The SRT consists of a wave-shaping element covered by a layer of explosive. The wave-shaping element generally looks like an isosceles triangle with a large base containing a nick. When the explosive is detonated, a pair of converging shockwaves at an angle to each other set off into the target object to be cut. The converging shockwaves collide in the material to be cut, which creates an enormous pressure. This pressure wave in the target is followed by a huge tensile stress wave when the two release waves (that follow the shock waves) interact. This creates a fracture in the material plane in which the shock and release waves interact [New Scientist 1986, 110(1504), 28]. In order to generate sufficiently powerful shockwaves, this method requires the use of so-called high explosives that have a detonation velocity of above 7 km/s. Transportation and storage of such high explosives is, however, bounded to severe safety rules and therefore impractical and very costly. In addition, the use of highly explosive materials is normally accompanied with the application of government permits.
It would be desirable to provide an alternative method of explosive cutting which allows at least partly overcoming drawbacks faced in the prior art.